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United States Patent |
6,239,246
|
Takahashi
,   et al.
|
May 29, 2001
|
Acrylic functional organopolysiloxanes and radiation-curable compositions
Abstract
A novel acrylic functional organopolysiloxane is obtained by effecting
addition reaction between (A) an organopolysiloxane having acrylic
functional groups and (B) an organopolysiloxane having a hydride group at
either end to induce partial crosslinking. The acrylic functional
organopolysiloxane forms a cured film ensuring light release and good
retention of adhesion.
Inventors:
|
Takahashi; Masatoshi (Gunma-ken, JP);
Ohba; Toshio (Gunma-ken, JP)
|
Assignee:
|
Shin-Etsu Chemical Co., Ltd. (Tokyo, JP)
|
Appl. No.:
|
361186 |
Filed:
|
July 27, 1999 |
Foreign Application Priority Data
| Jul 31, 1998[JP] | 10-230286 |
Current U.S. Class: |
528/32; 428/447; 522/99; 528/15; 528/31 |
Intern'l Class: |
C08G 077/20 |
Field of Search: |
522/99
528/15,31,32
428/447
|
References Cited
U.S. Patent Documents
4585669 | Apr., 1986 | Eckberg.
| |
5982041 | Nov., 1999 | Mitani et al.
| |
Foreign Patent Documents |
7316517 | Dec., 1995 | JP.
| |
Primary Examiner: Dawson; Robert
Assistant Examiner: Zimmer; Marc S.
Attorney, Agent or Firm: Birch, Stewart, Kolasch & Birch, LLP
Claims
What is claimed is:
1. An acrylic functional organopolysiloxane obtained by effecting addition
reaction between (A) an organopolysiloxane having acrylic functional
groups and (B) an organopolysiloxane having a hydride group at either end
to induce partial crosslinking, wherein some of the acrylic functional
groups on the organopolysiloxane (A) add to the hydride (SiH) groups at
both ends of the organopolysiloxane (B), with the non-added acrylic
functional groups on the organopolysiloxane (A) being left behind so that
the proportion of acrylic group-containing siloxane units is 2 to 40 mol %
in the entire siloxane units of the acrylic functional organopolysiloxane.
2. The organopolysiloxane of claim 1 wherein the organopolysiloxane (A) is
an organopolysiloxane having acrylic functional groups represented by the
following average compositional formula (1):
A.sub.x R.sup.1.sub.y SiO.sub.(4-x-y)/2 (1)
wherein A is --R.sup.2 OCOCR.sup.3.dbd.CH.sub.2 or --OR.sup.2
OCOCR.sup.3.dbd.CH.sub.2 wherein R.sup.2 is an alkylene group of 1 to 10
carbon atoms, and R.sup.3 is hydrogen or methyl,
R.sup.1 is independently a monovalent hydrocarbon group of 1 to 10 carbon
atoms,
x is from 0.002 to 1.50, y is 0 to 3.0, and the sum of x and y is from 1.5
to 2.5.
3. The organopolysiloxane of claim 1 wherein the organopolysiloxane (B) is
an organopolysiloxane having a hydride group at either end represented by
the following average compositional formula (2):
H(R.sub.2 SiO).sub.n SiR.sub.2 H (2)
wherein R is independently a monovalent hydrocarbon group of 1 to 10 carbon
atoms, and n is a positive number so that the organopolysiloxane has a
viscosity of 1 to 1,000,000 centistokes at 25.degree. C.
4. A radiation-curable composition comprising the acrylic functional
organopolysiloxane of claim 1 as a main component.
5. The composition of claim 4 further comprising a photo-initiator.
6. The organopolysiloxane of claim 1, wherein the organopolysiloxane (A) is
selected from the group consisting of formulae (3), (4), (5), (6), and
(7):
##STR7##
wherein A is --R.sup.2 OCOCR.sup.3.dbd.CH.sub.2 or --R.sup.2
OCOCR.sup.3.dbd.CH.sub.2, wherein R.sup.2 is an alkylene group of 1 to 10
carbon atoms, and R.sup.3 is hydrogen or methyl group, R.sup.1 is
independently a monovalent hydrocarbon group of 1 to 10 carbon atoms, p is
an integer of at least 2, q is an integer of at least 0, r and t are
integers of at least 0 and the sum of r+t is an integer of at least 2, s
and u are integers of at least 0 and the sum of s+u is an integer of at
least 0, and m is an integer of 0 to 3.
7. The organopolysiloxane of claim 1, wherein the acrylic functional
organopolysiloxane is selected from the group consisting of formulae (8),
(9), (10), (11), (12), and (13):
##STR8##
wherein A is --R.sup.2 OCOCR.sup.3.dbd.CH.sub.2 or --OR.sup.2
OCOCR.sup.3.dbd.CH.sub.2, wherein R.sup.2 is an alkylene group of 1 to 10
carbon atoms, and R.sup.3 is hydrogen or methyl group, R.sup.1 is
independently a monovalent hydrocarbon group of 1 to 10 carbon atoms, p is
an integer of at least 2, q is an integer of at least 0, r and t are
integers of at least 0 and the sum of r+t is an integer of at least 2, s
and u are integers of at least 0 and the sum of s+u is an integer of at
least 0, and m is an integer of 0 to 3.
Description
This invention relates to acrylic functional organopolysiloxanes useful as
a main component in back coating agents for adhesive tapes and release
paper coating agents for adhesive labels, and radiation-curable
compositions comprising the same.
BACKGROUND OF THE INVENTION
One common approach taken for the purpose of preventing adhesion and bond
between a substrate such as paper, converted paper or plastic film and a
pressure-sensitive adhesive material is to apply a curable silicone
composition onto the substrate surface and cure the coating with heat, UV
or electron beams. The coated substrate is generally known as a release
sheet.
The composition from which a releasable cured film is formed is required to
cure at a low temperature and within a short time from the standpoints of
productivity and energy saving and also in consideration of its
application to less heat resistant substrates. Especially from the
standpoint of preventing the substrate from deforming by heat, it is
advantageous to cure a coating with radiation such as electron beams or
ultraviolet rays into a cured film.
One useful method for preparing a composition for forming a releasable
cured film is to cure an organopolysiloxane having (meth)acrylate groups
by irradiating electron beams. The release of a cured film from a tacky
material depends on the (meth)acrylate group content of the (meth)acrylate
group-containing organopolysiloxane. The cured film requires a greater
peeling force as the content of (meth)acrylate groups increases.
On the other hand, at least a certain amount of (meth)acrylate groups is
necessary in order to quickly form a cured film. No cured film can be
formed if the (meth)acrylate group content is reduced. Also,
(meth)acrylate groups contribute to the phenomenon that a cured film
firmly bonds to the substrate. An organopolysiloxane having a reduced
(meth)acrylate group content cannot form a releasable film on the
substrate because the cured film will readily separate from the substrate.
As understood from the foregoing, the releasable cured film involves
contradictory release, cure, and substrate bond behaviors. It is difficult
to find a compromise between light peeling and formation of a satisfactory
cured film.
JP-A 7-316517 discloses that a cured film ensuring light peeling and age
stability is obtainable by mixing an organopolysiloxane having
(meth)acrylate groups with a non-reactive organopolysiloxane. In this
cured film, however, the non-reactive organopolysiloxane which has not
been incorporated in the crosslinked structure migrates from the surface
of the cured film to a surface in contact therewith, detracting from the
residual bonding force and ball tack, that is, the tack of a self-adhesive
layer.
SUMMARY OF THE INVENTION
An object of the invention is to provide an acrylic functional
organopolysiloxane which offers light release and good retention of
adhesion and is radiation curable. Another object of the invention is to
provide a radiation-curable composition comprising the same.
The invention provides an acrylic functional organopolysiloxane obtained by
effecting addition reaction between (A) an organopolysiloxane having
acrylic functional groups and (B) an organopolysiloxane having a hydride
(SiH) group at either end to induce partial crosslinking. This acrylic
functional organopolysiloxane is useful as a main component in back
coating agents for adhesive tapes and release paper coating agents for
adhesive labels. A radiation-curable composition comprising the
organopolysiloxane as a main component is lightly releasable, ensures good
retention of adhesion, and upon exposure to radiation, forms a cured film.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The acrylic functional organopolysiloxane of the invention is obtained by
effecting addition reaction between (A) an organopolysiloxane having
acrylic functional groups and (B) an organopolysiloxane having a hydride
group at either end to induce partial crosslinking.
The organopolysiloxane (A) is preferably an organopolysiloxane having
acrylic functional groups represented by the following average
compositional formula (1):
A.sub.x R.sup.1.sub.y SiO.sub.(4-x-y)/2 (1)
wherein A is --R.sup.2 OCOCR.sup.3.dbd.CH.sub.2 or --OR.sup.2
OCOCR.sup.3.dbd.CH.sub.2 wherein R.sup.2 is an alkylene group of 1 to 10
carbon atoms, and R.sup.3 is hydrogen or methyl; R.sup.1, which may be the
same or different, is a monovalent hydrocarbon group, of 1 to 10 carbon
atoms; x is from 0.002 to 1.50, y is 0 to 3.0, and the sum of x and y is
from 1.5 to 2.5.
Preferred examples of the C.sub.1 -C.sub.10 alkylene group represented by
R.sup.2 are methylene, ethylene and propylene groups.
The groups represented by R.sup.1 are substituted or unsubstituted
monovalent C.sub.1 -C.sub.10 hydrocarbon groups, for example, alkyl groups
such as methyl, ethyl, propyl and butyl, cycloalkyl groups such as
cyclohexyl, aryl groups such as phenyl and tolyl, aralkyl groups such as
benzyl and phenylethyl, and substituted ones of these groups in which some
or all of the hydrogen atoms attached to carbon atoms are replaced by
hydroxyl groups, cyano groups or halogen atoms, such as hydroxypropyl,
cyanoethyl, 1-chloropropyl and 3,3,3-trifluoropropyl. Alkyl and aryl
groups are desirable as R.sup.1 groups when the release of the acrylic
functional organopolysiloxane in the cured state is taken into account.
Among the organopolysiloxanes of formula (1), those of the following
formulae (3) to (7) are preferred.
##STR1##
In formulae (3) to (7), p is an integer of at least 2, preferably 2 to 100
and more preferably 2 to 50, q is an integer of at least 0, preferably 0
to 1,000 and more preferably 0 to 500. Letters r and t are integers of at
least 0 and the sum of r+t is an integer of at least 2, preferably 2 to
100 and more preferably 2 to 50; s and u are integers of at least 0 and
the sum of s+u is an integer of at least 0, preferably 0 to 2,000 and more
preferably 0 to 1,000; and m is an integer of 0 to 3.
The organopolysiloxane (A) generally has a viscosity of 10 to 10,000
centistokes at 25.degree. C. and preferably 50 to 1,000 centistokes at
25.degree. C.
Specific examples of the organopolysiloxane (A) are given below.
##STR2##
The organopolysiloxane (A) may be used alone or in admixture of two or
more.
The organopolysiloxane having a hydride group at either end (B) is
preferably one represented by the following average compositional formula
(2):
H(R.sub.2 SiO).sub.n SiR.sub.2 H (2)
wherein R, which may be the same or different, is a monovalent hydrocarbon
group of 1 to 10 carbon atoms, and n is a positive number so that the
organopolysiloxane has a viscosity of 1 to 1,000,000 centistokes at
25.degree. C.
Illustrative of the groups represented by R are substituted or
unsubstituted monovalent C.sub.1 -C.sub.10 hydrocarbon groups, for
example, alkyl groups such as methyl, ethyl, propyl and butyl, cycloalkyl
groups such as cyclohexyl, aryl groups such as phenyl and tolyl, and
substituted ones of these groups in which some or all of the hydrogen
atoms attached to carbon atoms are replaced by hydroxyl groups, cyano
groups or halogen atoms, such as hydroxypropyl, cyanoethyl, 1-chloropropyl
and 3,3,3-trifluoropropyl. Alkyl and aryl groups are desirable as R groups
when the release of the acrylic functional organopolysiloxane in the cured
state is taken into account. Further preferably, at least 80 mol % of the
R groups in the entire siloxane units are methyl groups. The letter n is a
positive number, preferably at least 2, so that the organopolysiloxane has
a viscosity of 1 to 1,000,000 centistokes, especially 50 to 1,000
centistokes at 25.degree. C.
Illustrative examples of the organopolysiloxane (B) are given below.
H(Me.sub.2 SiO).sub.50 SiMe.sub.2 H
H(Me.sub.2 SiO).sub.100 SiMe.sub.2 H
H(Me.sub.2 SiO).sub.200 SiMe.sub.2 H
H(Me.sub.2 SiO).sub.100 (Ph.sub.2 SiO).sub.20 SiMe.sub.2 H
Herein, Me is methyl and Ph is phenyl.
The organopolysiloxane (B) may be used alone or in admixture of two or
more.
For reaction, the organopolysiloxane having acrylic functional groups (A)
and the organopolysiloxane having a hydride group at either end (B) are
preferably used in a molar ratio (B)/(A) from 99/1 to 5/95 and especially
from 98/2 to 20/80. An excessive amount of the organopolysiloxane (B)
would result in losses of light release and slip whereas a too less amount
of the organopolysiloxane (B) would result in losses of cure and adhesion
retention. The number of molecules of the acrylic functional
group-containing organopolysiloxane (A) is preferably at least 2 times,
more preferably 2 to 100 times the number of molecules of the hydride
group-containing organopolysiloxane (B). Further preferably, the
organopolysiloxanes (A) and (B) are used such that the molar ratio of
CH.sub.2.dbd.CR.sup.3 groups/hydride groups (SiH groups) is at least 2,
and especially from 2 to 100.
The acrylic functional organopolysiloxane according to the invention is
obtained by effecting addition reaction between the organopolysiloxanes
(A) and (B) to induce partial crosslinking. For the addition reaction,
catalysts are used. Preferred addition reaction catalysts are platinum
catalysts including chloroplatinic acid, alcohol solutions of
chloroplatinic acid, reaction products of chloroplatinic acid with
alcohols, reaction products of chloroplatinic acid with olefinic
compounds, and reaction products of chloroplatinic acid with
vinyl-containing siloxanes. Other common addition reaction catalysts such
as rhodium and ruthenium catalysts are also useful. The amount of the
catalyst added is not critical although an appropriate amount is 0.01 to
10% of the weight of the acrylic functional group-containing
organopolysiloxane (A) and the hydride group-containing organopolysiloxane
(B) combined. Differently stated, an appropriate amount of the catalyst is
such that the molar ratio of SiH groups/Pt (or Rh or Ru) is from 10.sup.2
/1 to 10.sup.6 /1.
Addition reaction may be effected at room temperature to 300.degree. C.
Heating above 50.degree. C. will promote the reaction. At too high
temperatures, acrylic functional groups can polymerize to form a gel.
Reaction temperatures below 150.degree. C. are preferred in this sense.
The reaction time is not critical although a time of 1 to 10 hours is
preferred.
Optionally addition reaction is carried out in a solvent. Exemplary
solvents are aromatic solvents such as toluene and xylene, aliphatic
solvents such as hexane and octane, ketone solvents such as methyl ethyl
ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate
and isobutyl acetate, ether solvents such as diisopropyl ether and
1,4-dioxane, and mixtures of any of these solvents. The use of a solvent
or a mixture of solvents in which the acrylic group-containing
organopolysiloxane (A) and the hydride group-containing organopolysiloxane
(B) are soluble is necessary for addition reaction to proceed efficiently.
Upon reaction, a stabilizer for preventing radical polymerization of
acrylic functional groups is added if desired.
As mentioned above, the acrylic functional organopolysiloxane according to
the invention is obtained by effecting addition reaction between the
organopolysiloxane having acrylic functional groups (A) and the
organopolysiloxane having a hydride (SiH) group at either end (B) to
induce partial crosslinking. Some of the acrylic functional groups on the
organopolysiloxane (A) add to the hydride (SiH) groups at both ends of the
organopolysiloxane (B), with the non-added acrylic functional groups on
the organopolysiloxane (A) being left behind. In the entire siloxane units
of the acrylic functional organopolysiloxane according to the invention,
the proportion of acrylic group-containing siloxane units is preferably 2
to 40 mol %, and more preferably 5 to 25 mol %. An organopolysiloxane with
less than 2 mol % of acrylic group-containing siloxane units would be
short in cure and adhesion retention whereas light release and slip would
become insufficient in excess of 40 mol %.
Illustrative examples of the acrylic functional organopolysiloxane
according to the invention are those of the following formulae (8) to
(13).
##STR3##
More specific examples of the acrylic functional organopolysiloxane are
those of the following formulae (14) to (17).
##STR4##
The acrylic functional organopolysiloxane according to the invention may be
used alone or in combination with another acrylic group-containing
organopolysiloxane having a different degree of polymerization to
formulate a radiation-curable organopolysiloxane composition. The
composition is obtained by uniformly mixing predetermined amounts of the
respective components. If necessary, organic resins such as acrylate
oligomers, agents for modifying adhesion to substrates, leveling agents,
antistatic agents, anti-foaming agents, pigments and other types of
organopolysiloxanes may be added. On use, the composition may be diluted
with organic solvents.
Adding a photopolymerization initiator to the composition yields a UV
radiation-curable organopolysiloxane composition. Useful photo-initiators
include initiators of the ring opening type, for example, acetophenone
compounds such as 2-hydroxy-2-methyl-1-phenylpropan-1-one,
1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,
1-hydroxycyclohexylphenylketone, and 2,2-dimethoxy-2-phenylacetophenone,
2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone, benzoyl diphenyl
phosphine oxide, and benzoin ether compounds such as benzoin isopropyl
ether and benzoin isobutyl ether; initiators of the hydrogen abstraction
type, for example, benzophenone, 2-isopropylthioxanthone, and
2-ethylanthraquinone. The amount of the initiator added may be 0.1 to 10
parts, desirably 1 to 5 parts by weight, per 100 parts by weight of the
radical-polymerizable organopolysiloxane. Less than 0.1 part of the
initiator would fail to achieve a cure rate whereas more than 10 parts
would detract from shelf stability.
Examples of the substrate to which the organopolysiloxane composition
according to the invention is applied include plastic films and sheets
made of synthetic resins such as polyesters, polypropylene, polyethylene,
polyvinyl chloride, polytetrafluoroethylene and polyimides, paper sheets
such as glassine paper, kraft paper and clay coated paper, and laminated
paper sheets such as polyethylene laminated wood-free paper and
polyethylene laminated kraft paper.
In applying the composition to the substrate, any of well-known techniques
such as roll coating, gravure coating, wire doctor coating, air knife
coating and dip coating may be used. A coating weight of 0.01 to 20.0
g/m.sup.2 is appropriate.
Upon exposure to radiation, the coating cures into a cured film. Examples
of effective radiation include electron beams, .alpha.-rays, .beta.-rays,
.gamma.-rays, and ultraviolet rays emitted from mercury arc lamps,
medium-pressure mercury lamps, high-pressure mercury lamps, and metal
halide lamps. The dose of radiation necessary to cure the coating may be
about 1 to 10 Mrad for electron beams. In the case of UV radiation, the
organopolysiloxane composition to which a photopolymerization initiator
has been added is exposed for 0.01 to 10 seconds under a 2-kW
high-pressure mercury lamp (80 W/cm) at a distance of 8 cm.
EXAMPLE
Examples of the invention are given below by way of illustration and not by
way of limitation. All parts are by weight. Physical properties are
measurements obtained by the following tests.
Peeling Force
An organopolysiloxane composition was applied onto an OPP web to a coating
weight of 1.0 g/m.sup.2. The EB curing equipment used was an electron beam
processor C-150 by ESI, which was operated at an accelerating voltage of
165 kV. With electron beams, the coating was cured at a dose of 3 Mrad and
an oxygen concentration below 100 ppm. The cured film was aged at
25.degree. C. for 20 hours. To the surface of this cured film, a hot-melt
adhesive coated kraft tape strip (5 cm wide) was attached. The test
assembly was aged at 50.degree. C. for 20 hours. Using a tensile tester,
the tape strip was peeled from the OPP web at an angle of 180.degree. and
a pulling rate of 0.3 m/min. A force (gf/5 cm) needed to peel the tape
strip was measured.
Retention of Adhesion
Like the peeling force test, a cured film of an organopolysiloxane
composition was formed on an OPP web and aged. An adhesive tape strip
Nitto No. 31B (trade name, Nitto Denko K.K.) was attached to the surface
of the cured film. With a load of 20 g/cm.sup.2 rested thereon, this
assembly was heat treated at 70.degree. C. for 20 hours. The tape strip
was peeled from the web and then attached to a stainless steel plate. A
force (gf/2.5 cm) needed to peel the tape strip from the stainless steel
plate was measured. A percentage of this force relative to a force needed
to peel the standard adhesive tape strip (untreated) was calculated. This
is a percent retention of adhesion.
Example 1
A four-necked flask equipped with a stirrer, thermometer, reflux condenser,
and dropping funnel was charged with 62.3 parts of toluene, 113 parts of
an acrylate group-containing organopolysiloxane represented by the average
compositional formula:
Me.sub.3 SiO--(A.sup.1 MeSiO).sub.6 --(Me.sub.2 SiO).sub.22 --SiMe.sub.3
wherein Me is --CH.sub.3 and A.sup.1 is --CH.sub.2 CH.sub.2 CH.sub.2
OCOCH.dbd.CH.sub.2, 0.934 part of 2,6-tert-butyl-4-methylphenol and 0.037
part of N,N'-diphenyl-1,4-phenylenediamine as polymerization inhibitors.
To the flask was added 3.12 parts of a 2% toluene solution of a platinum
catalyst. The flask was heated to 80.degree. C. whereupon 73.9 parts of an
organopolysiloxane having hydride groups at both ends was added dropwise
over one hour. This organopolysiloxane was represented by the following
formula:
H(Me.sub.2 SiO).sub.99 --SiMe.sub.2 H
and had a viscosity of 120 centipoises at 25.degree. C.
After the completion of dropwise addition, the reaction solution was
stirred for 4 hours at 90.degree. C. The reaction solution was allowed to
cool to room temperature, and with 25.0 parts of activated carbon added,
stirred overnight. After the activated carbon was removed by filtration,
the toluene and volatiles were distilled off at 80.degree. C. and 2 Torr.
There was obtained 159 parts of Sample 1 represented by the following
formula. Sample 1 had a viscosity of 293 centipoises and a refractive
index of 1.417, and the conversion of terminal hydride groups was 100%. On
analysis by GPC and .sup.29 Si NMR, Sample 1 was identified to be a
composition consisting of a crosslinked product (X) and a non-crosslinked
product (Y) in a weight ratio X/Y of 70/30. Although this sample is deemed
to contain some products of crosslinked acrylic groups, the crosslinked
product (X) is mainly of the following structure and the non-crosslinked
product (Y) is of the following structure.
##STR5##
The peeling force and adhesion retention of a film obtained by curing the
organopolysiloxane were measured by the above tests, with the results
shown in Table 1.
Comparative Example 1
Sample 2 was obtained by mixing 113 parts of the acrylate group-containing
organopolysiloxane and 73.9 parts of the organopolysiloxane having hydride
groups at both ends, which were the same as used in Example 1. This
composition did not cure under the irradiating conditions of the test. The
peeling force and adhesion retention of this composition were measured by
the above tests, with the results shown in Table 1.
Comparative Example 2
Sample 3 was an acrylate group-containing organopolysiloxane of the average
compositional formula:
A.sup.2 Me.sub.2 SiO--(A.sup.1 MeSiO).sub.18 --(Me.sub.2 SiO).sub.80
--SiMe.sub.2 A.sup.2
wherein Me is --CH.sub.3, A.sup.1 is --CH.sub.2 CH.sub.2 CH.sub.2
OCOCH.dbd.CH.sub.2, and A.sup.2 is --CH.sub.2 OCOCH.dbd.CH.sub.2. The
peeling force and adhesion retention of a cured film of the
organopolysiloxane were measured by the above tests, with the results
shown in Table 1.
Example 2
A composition was obtained by mixing 20 parts of Sample 1 with 80 parts of
Sample 3. The peeling force and adhesion retention of a cured film of the
composition were measured by the above tests, with the results shown in
Table 1.
Example 3
A composition was obtained by mixing 10 parts of Sample 1 with 90 parts of
Sample 3. The peeling force and retention of adhesion of a cured film of
the composition were measured by the above tests, with the results shown
in Table 1.
Comparative Example 3
A composition was obtained by mixing 20 parts of Sample 2 with 80 parts of
Sample 3. This composition was repellent on the web and failed to provide
a smooth surface upon curing. The peeling force and adhesion retention of
a cured film of the composition were measured by the above tests, with the
results shown in Table 1.
Comparative Example 4
A composition was obtained by mixing 20 parts of an acrylate
group-containing organopolysiloxane with 80 parts of Sample 3. The peeling
force and adhesion retention of a cured film of the composition were
measured by the above tests, with the results shown in Table 1.
The acrylate group-containing organopolysiloxane used herein has an
approximately equal acrylic equivalent to Samples 1 and 2 and is
represented by the following average compositional formula.
##STR6##
TABLE 1
Peeling force Retention of adhesion
(gf/5 cm) (%)
Example 1 9 88
Example 2 48 93
Example 3 98 98
Comparative Example 1 3 70
Comparative Example 2 450 98
Comparative Example 3 48 70
Comparative Example 4 270 98
There have been described acrylic functional organopolysiloxanes which will
form releasable cured films ensuring light release and good retention of
adhesion.
Japanese Patent Application No. 10-230286 is incorporated herein by
reference.
Although some preferred embodiments have been described, many modifications
and variations may be made thereto in light of the above teachings. It is
therefore to be understood that the invention may be practiced otherwise
than as specifically described without departing from the scope of the
appended claims.
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